Resonance-Enabled Drills, Resonance Gauges, and Related Methods

ABSTRACT

Provided herein is a resonance-enabled drill, comprising a housing; one or more force generators chosen from one or more voice coil actuators, one or more eccentrics driven by one or more electric motors, or combinations thereof; one or more sonic heads coupled to the one or more force generators; a plurality of springs coupling the housing to the one or more sonic heads; and a drill rod disposed on its proximal end to the one or more sonic heads. Also provided is a gauge for a sonic drill configured to display information to an operator, for example indicating to the operator when the drill is on or near resonance. Further provided are methods for selecting a resonance frequency in a sonic drill.

RELATED METHODS

This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 63/159,435 filed Mar. 10, 2021, the disclosure of which is incorporated by reference in its entirety for all purposes.

The present disclosure generally relates to machines that use resonance to transfer energy from the machine to a drill bit or bottom hole assembly to penetrate the earth, concrete, or any material to drill a hole or take a sample.

Generally, sonic drills have used counterrotating eccentrics mechanically timed to generate vertical forces while canceling the horizontal forces. The eccentrics are typically driven directly from an internal combustion engine or by an internal combustion engine driving hydraulics, which have response times longer than the penetration systems response time constant. A throttle controls these systems by engine speed or a valve or driven pump speed.

Hydraulic controls have a slow response time, making the drill hard to control by hand. As the frequency increases and the drill approaches resonance, the system requires less input power, which causes the eccentrics rotation speed to increase. As a result, the system is pulled into the resonant condition. The operator nor the hydraulic system can respond fast enough to avoid speeding up into the resonant peak and remaining on the resonant peak.

What is needed is a resonance-enabled drill with quick response times and finer control so that the drill can stay at the recommended resonance frequency or desired operating condition

SUMMARY

The present disclosure provides a resonance-enabled drill, comprising a housing; one or more force generators chosen from one or more voice coil actuators, one or more eccentrics driven by one or more electric motors, or combinations thereof; one or more sonic heads coupled to the one or more force generators; a plurality of springs coupling the housing to the one or more sonic heads; and a drill rod disposed on its proximal end to the one or more sonic heads.

In certain embodiments, the drill further comprises a bit disposed on the distal end of the drill rod.

In certain embodiments, the one or more voice coil actuators comprise a coil assembly rigidly disposed on the housing or on a reflection mass, and a magnet assembly disposed on the one or more sonic heads. In certain embodiments, the coil assembly of each of the one or more voice coil actuators has little to no motion compared to the one or more sonic heads.

In certain embodiments, each eccentric is driven by one electric motor. In certain embodiments, the one or more force generators comprise two paired sets of eccentrics configured to exert no vertical force, using a 180° phase angle between the two paired sets of eccentrics. In certain embodiments, the one or more force generators comprise two paired sets of eccentrics configured to exert full vertical force, using a 0° phase angle between the two paired sets of eccentrics.

In certain embodiments, the drill further comprises a seal disposed between the housing and the drill rod.

In certain embodiments, the drill further comprises a spring-damper disposed between the drill rod and the bit. In certain embodiments, the spring-damper cushions impact of the drill bit by widening and lowering the impulse magnitude, whereby transfer of primary resonant energy to unwanted resonant modes is lowered, and the drill bit is kept in motion and not fused with a workpiece.

In certain embodiments, the drill further comprises an energy transfer rod and flange adaptor disposed between the one or more sonic heads and the drill rod.

In certain embodiments, the drill further comprises a rotor, stator, and stator housing disposed between the one or more sonic heads and the drill rod. The rotor is disposed on the drill string and the stator and stator housing each disposed on the housing, thus allowing the sonic drill rod to rotate. In certain embodiments, this configuration induces torsional resonances when the input force is oscillated on the rotary motor. In these embodiments, between the one or more sonic heads and the adapter, when present, a rotor provide rotation torques onto the pipe. A decoupler/stator can also be between the rotation of the pipe and the one or more sonic heads, which are stationary. In one configuration, the rotor, stator, and stator housing are tied together so that the drill rod does not rotate but can oscillate from the input torque at the rotor.

In certain embodiments, the kinetic energy stored in the drill by the one or more sonic heads is directly offset by potential energy stored within the plurality springs. In certain embodiments, the drill further comprises a reflection mass coupled to the one or more sonic heads through a second plurality of springs and configured to offset the kinetic energy stored in the drill.

In certain embodiments, the housing comprises a plurality of plates and a plurality of standoffs. In certain embodiments, during operation, the drill has a resonance frequency and, when on resonance, an alternating input force is in phase with the oscillation velocity of the one or more sonic heads. In certain embodiments, the oscillating input force is provided from the spinning eccentrics or voice coil force. In these embodiments, the force is not constant but rather oscillates (or alternates) up and down.

The present disclosure also provides a gauge for a sonic drill configured to display information to an operator when the drill is on or near resonance. The sonic drill may be any resonance-enabled drill disclosed herein. In certain embodiments, the information comprises one or more parameters chosen from an amplitude of the drill bit, a resonant frequency of the drill, a stress state, power components of the drill, and safe operating frequencies.

In certain embodiments, the gauge indicates one or more positions chosen from bit decoupling, a lower recommended range, a recommended operating condition, a high recommend range, and fusion. In certain embodiments, the power components of the drill comprise useful power, power delivered at the bit, power absorbed along the drill string's length, energy stored in the drill, and wasted power.

In certain embodiments, the gauge is further configured to display to the operator where mechanical resonance is located compared to operating conditions of the drill.

In certain embodiments, the gauge is further configured to show the ratio of bit motion to motion of the one or more sonic heads.

In certain embodiments, when penetration of the drill slows or ceases, the gauge is configured to display potential problems with options to remedy the lower-than-desired penetration rate.

Any resonance-enabled drill disclosed herein may comprise any gauge disclosed herein.

The present disclosure further provides a method for selecting a resonance frequency in a sonic drill comprising a force generator, one or more sonic heads, and a gauge. The phase is measured between a force generator and one or more sonic heads in the sonic drill. A resonance frequency is selected based on the phase displayed on a gauge to indicate the relative position of the phase for resonance of the sonic drill. In certain embodiments, phase between the force generator and the one or more sonic heads in the sonic drill is measured and resonance on the gauge is displayed to indicates where the resonance frequency is relative to the current operating frequency of the drill based on the phase measurement.

In certain embodiments, when the sonic drill comprises a bit, the method further comprises maximizing the ratio between the bit motion and the motion of the one or more sonic heads. In certain embodiments, when the sonic drill comprises a bit and penetration of the bit is slowed or ceased, the method further comprises reducing the weight on the bit to adjust the resonance frequency of the drill to continue drilling.

In certain embodiments, the method further comprises estimating the stress state of the drill. In certain embodiments, the sonic drill selects the resonance frequency when an operating condition changes. In certain embodiments, the operating condition is chosen from pipe length, the ratio between the drill bit motion and the motion of the one or more sonic heads, weight on the bit, or the workpiece.

In certain embodiments, weight applied to the bit is greater when drilling a workpiece with a lower soil stiffness than when drilling a workpiece with a greater soil stiffness. In certain embodiments, critical weight on the bit is pushed up to allow motion at the drill bit to perform drilling. In certain embodiments, as soil stiffness increases, less weight on bit is required for fusing. In certain embodiments, weight on the bit is inversely proportional to soil stiffness.

In certain embodiments, the weight applied to the bit is great enough to provide fusing with the soil. The bit boundary condition changes from free to fused with the soil. The soil stiffness and viscous damping are now a part of the sonic drill system. The drill system turns into a sensor to measure the soil stiffness and viscous damping at the drill bit.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements. The drawings provide exemplary embodiments or aspects of the disclosure and do not limit the disclosure's scope.

FIG. 1 shows a resonance-enabled drill comprising a voice coil and a sonic head.

FIG. 2 shows a top perspective cross-section of a voice coil in a resonance-enabled drill.

FIG. 3 shows a side plan view cross-section of the resonance-enabled drill of FIG. 2.

FIG. 4 shows a side plan view of the resonance-enabled drill of FIG. 2.

FIG. 5 shows a top plan view of the resonance-enabled drill of FIG. 2.

FIG. 6 shows a resonance-enabled drill with two voice coil actuators coupled on the same side of a sonic head.

FIG. 7 shows a resonance-enabled corer with a core barrel assembly to take soil samples.

FIG. 8 shows a resonance-enabled corer with a core barrel assembly and two sonic heads.

FIG. 9 shows a resonance-enabled corer with a core barrel assembly to take soil samples with a configuration to cancel forces to the housing with opposing voice coils to cancel resultant forces to the housing.

FIG. 10 shows the percent force with phasing two eccentric pairs from in-phase (0°) to out of phase (180°).

FIG. 11 shows the phasor vector relation of the resultant force generated between two sinusoidal forcing functions from one force phased relative to the other.

FIG. 12 shows a meter that displays the current state of the drill compared to the closest system resonance.

FIG. 13 shows the mode shape of (C) the displacement, (D) acceleration, and (E) stress of the drill system for (A) different lengths and (B) input frequencies. This example displays a single frequency and system length configuration, but the system's length and frequency may be adjusted.

FIG. 14 shows the (B) displacement and (C) acceleration amplitudes of the head and bit versus the input frequency. The plots may be swept through various lengths of pipe (A).

FIG. 15 shows a table of the resonant frequencies (in Hertz) of the penetration system relative to the number of added sections of drill pipe.

FIG. 16 shows (B) the plot of input power, useful power, wasted power, and power is delivered to the bit over the operating frequencies of the penetration system. (A) The length of pipes can also be selected. (C) Acceleration of the head and bit is also plotted on the lower axis and Input Power vs. Input Frequency.

FIG. 17 shows a plot indicating where resonance is located, stable operating conditions, and unstable operation conditions for a hydraulically driven eccentric penetration system.

FIG. 18 shows the safe operating frequencies in white, where the operations conditions are shaded where the system stress state is too great, and failures will likely occur.

FIG. 19 shows an eccentric-driven sonic drill, where the eccentrics are counterrotating and timed together.

FIG. 20 shows a dual electric motor drive for a dual eccentric sonic drill. Each motor drives a single spinning eccentric.

FIG. 21 shows four electric motor drives for a four eccentric sonic drill organized as two paired sets of eccentrics.

FIG. 22 shows the potential energy and kinetic energy changes of a resonant system of FIG. 21 as a function of time.

FIG. 23 shows the energy when the resonant system of FIG. 21 operates at a frequency below mechanical resonance.

FIG. 24 shows a single electric motor drive for a dual eccentric sonic drill, where the eccentrics are mechanically timed to each other. A rotor and stator drive the rotational or torsional vibration of the pipe, allowing the pile to not rotate but to oscillate instead.

FIG. 25 shows (B) a plot of displacement amplitude and (C) acceleration of the head and bit versus frequency. (A) The length of pipes can also be selected.

FIG. 26 shows a meter that displays the current state of the drill bit compared to decoupled and fusion.

FIG. 27 shows a resonance-enabled machine configured as a drill with a voice coil-driven system at the sonic head.

FIG. 28 displays a critical weight on bit gauge.

FIG. 29 displays that when the sonic drill was operated at nominally constant frequency of 120 Hz between 245 seconds and 250 seconds, the weight on bit affected the system performance.

FIG. 30 shows that a higher penetration rate was observed when the weight on bit was below the critical weight on bit.

FIG. 31 shows the tangents of the penetrations rates from FIG. 30.

FIG. 32 displays the relative push-and-pull forces from the hydraulic cylinder of the sonic drill that lift and push down the sonic drill.

FIG. 33 shows the resonance meter gauge readings during testing with a GeoProbe 8150 LS using 40 ft of 4″ drill pipe and a coring bit.

FIG. 34 is a schematic showing the top and bottom boundary conditions operating on the drill string of a drill rig with a sonic driver.

FIG. 35 shows the phase between input force and the measured head acceleration of a sonic drill as a function of frequency. The phases at 104.5 Hz are marked for (A) no coupling at the bit, (B) full coupling with sand, (C) full coupling with stiff clay, and (D) full coupling with granite.

Table 1 lists reference numerals used throughout the figures and this disclosure.

TABLE 1 Reference numerals 100 drill 105 energy absorbed within the system 115 peak-to-peak energy absorbed within the system amplitude 150 corer 200 sonic heads 205 kinetic energy 210 first sonic head 215 motion of first sonic head 220 second sonic head 225 motion of second sonic head 230 (internal force) reflection mass 300 housing 310 first housing plate 312 housing ledge 320 second housing plate 330 housing shell 350 standoff 351 fastener 400 springs 405 potential energy 410 housing-to-first sonic head spring 420 housing-to-second sonic head spring 430 first-to-second sonic head spring 440 housing-to-reflection mass springs 500 voice coil actuator 510 first coil assembly 515 first magnet assembly 520 second coil assembly 525 second magnet assembly 530 first eccentric 540 second eccentric 530, 540 first plurality of eccentrics 550 third eccentric 560 fourth eccentric 550, 560 second plurality of eccentrics 600 pile/drill rod/drill string 610 seal 620 spring-damper 630 bit 640 energy transfer rod 650 flange adaptor 660 core barrel 670 corer bit 680 stator 683 stator housing 685 rotor 700 the workpiece (concrete, strata, etc.) 800 motors 810 first motor 815 first coupling 820 second motor 825 second coupling 830 third motor 835 third coupling 710 core 840 fourth motor 845 fourth coupling k₁ first spring constant k₂ second spring constant k₃ third spring constant k_(x) reflection mass spring constant

DETAILED DESCRIPTION Resonance-Enabled Drill

A “resonance-enabled drill” is a type of resonance-enabled machine, such as a sonic drill or sonic penetration device, within this disclosure. Generally, within this disclosure, “drill,” “sonic drill,” and “resonance-enabled drill” are used interchangeably. In certain embodiments, the drill is configured to function as a corer and can also be referred to as a “resonance-enabled corer.”

Resonance is defined as when an oscillation system over a single oscillation cycle the stored energy of the drill matches the kinetic energy stored in the drill and that results in the force being in phase with the resultant velocity. By the definition of resonance, a person of skill in the art would readily understand how the drill operates. For example, when the system is on resonance, an alternating input force is in phase with the system oscillation velocity of the one or more sonic heads.

To slow a hydraulically driven eccentric system, finer controls may be used for the flow driving the eccentrics. In certain embodiments, an energy-absorbing device, such as a brake or generator, may limit the speed. The system can reduce the input power to keep the input frequency below resonance. Disclosed herein is another method wherein an electric motor drives the counterrotating eccentrics. In certain embodiments, the motor is closed-loop controlled to control the speed. In certain embodiments, a motor brakes the system's speed so that the eccentrics can spin at any desired rate.

The resonance-enabled drills disclosed herein comprise a force generator, such as one or more voice coil actuators or one or more pairs of eccentrics.

Voice Coil Actuators

A voice coil actuator commonly drives mechanical systems with linear motion. The coil assembly is disposed on the sonic head because it is lighter than the magnet assembly and losses from the inertia of the oscillating mass prevent the heavier mass from being the sonic head. Examples include loudspeakers to generate sound/music. Care has been taken to reduce the coil assembly's weight mounted to the speaker to provide the best performance with the highest efficiency.

With the coil moving, power wires delivering current to the coil are always being fatigued, limiting the life for the voice coil and the power wires delivering current to the coil. As disclosed herein, the voice coil is mounted to housing to mitigate fatigue and increase reliability. Still, up to now, this configuration caused reduced performance and lower efficiency. By configuring the voice coil assembly in a resonance-enabled drill, the kinetic energy stored in the drill by the voice coil assemblies' moving masses is directly offset by potential energy stored within the drill's springs. Therefore, heavier voice coil assemblies can be mounted on a sonic head of the resonance-enabled drill without losing performance or efficiency.

The one or more sonic heads are configured to operate on a resonant mode shape. The one or more sonic heads are out of phase of one another. Each of the one or more sonic heads is coupled to the housing through a plurality of springs. When more than one sonic head is present, the sonic heads are also coupled with each other through a second plurality of springs. The drill is configured so that the forces transferred to the housing through the coupling springs between the one or more sonic heads and the housing are at or near zero over the drill's operating range around its resonant frequency.

In resonance-enabled drills driven by a voice coil, the range of frequencies can and will vary. A person of skill in the art understands to select a frequency range suitable for operating the resonance-enabled drill under the conditions needed for the selected workpiece. For example, the voice coil may operate between 60 Hz and 2,000 Hz (2 kHz), such as between 60 Hz and 100 Hz, between 100 Hz and 200 Hz, between 200 Hz and 300 Hz, between 300 Hz and 400 Hz, between 400 Hz and 500 Hz, between 500 Hz and 600 Hz, between 600 Hz and 700 Hz, between 700 Hz and 800 Hz, between 800 Hz and 900 Hz, between 100 Hz and 1 kHz, between 1 kHz and 1.1 kHz, between 1.1 kHz and 1.2 kHz, between 1.2 kHz and 1.3 kHz, between 1.3 kHz and 1.4 kHz, between 1.4 kHz and 1.5 kHz, between 1.58 kHz and 1.6 kHz, between 1.6 kHz and 1.7 kHz, between 1.7 kHz and 1.8 kHz, between 1.8 kHz and 1.9 kHz, or between 1.9 kHz and 2 kHz. In certain embodiments, the frequency is greater than 60 Hz. In certain embodiments, the frequency is less than 2 kHz. In certain embodiments, the frequency is between 60 Hz and 250 Hz, such as between 60 Hz and 150 Hz.

FIG. 1 shows a resonance-enabled drill 100, comprising a housing 300, a sonic head 210 coupled to the housing 300 by a first plurality of springs 410, a coil assembly 510 disposed on the housing 300, a voice coil magnet assembly 515 coupled to the sonic head 210, a drill rod 600 disposed on the proximal end to the sonic head 210 and on the distal end to a bit 630. A seal 610 is disposed between the drill rod 600 and the housing 300. The voice coil actuator 500 comprises a coil assembly 510 and a magnet assembly 515. In this embodiment of the single sonic head resonance-enabled drill 100, the voice coil magnet assembly 515 is disposed beneath and coupled to the sonic head 210. During operation, the bit 630 contacts the workpiece 700, which can be soil, strata, rock formation, concrete, or other natural or manmade feature, to form a borehole.

Optionally, the resonance-enabled drill 100 further comprised a spring-damper 620 disposed between the drill rod 600 and the bit 630. The spring-damper 620 widens or flattens the impulse load from the drill bit 630. For example, if a resonance-enabled drill 100 made of only steel impacts a rock formation 700, the formation has infinite impedance and reflects the impact fully onto the drill rod 600. The impact creates an impulse load and excites all resonant frequencies of the resonant system. With repeated blows, the energy quickly transitions from the primary resonant mode to a broadband of resonant frequencies, fusing the drill bit 630 with the formation 700.

By disposing a spring-damper 620 (with or without internal damping) between the drill bit 630 and the drill rod 600, the bit 630 can move with the end of the drill rod 600 during normal operation. When a hard substrate is encountered and impulse loads are generated, the spring-damper 620 cushions the impact by widening and lowering the impulse magnitude. This lowers the transfer of the primary resonant energy to unwanted resonant modes, keeping the drill bit 630 in motion and not fused with the strata 700. The bit's 630 susceptibility to fusing is lessened, the useful range of weight on bit 630 is widened, and the acceleration force and energy onto the bit 630 are lessened during drilling, causing less wear and extending the service life.

In certain embodiments, the spring-damper 620 comprises a resilient member, such as a spring or a viscoelastic medium. The damping within the spring-damper 620 is rate-dependent. When present, the spring gives. The load through the transient impact transfers by the damping or viscous part of the viscoelastic medium.

Referring to FIGS. 2-5, the housing 300 comprises a first housing plate 310 and a second housing plate 320. The sonic head 210 is coupled to the first housing plate 310 by a plurality of housing-to-sonic head springs 410. The sonic head 210 is coupled to the second housing plate 320 by a second plurality of housing-to-sonic head springs 410.

In certain embodiments, the resonance-enabled drill further comprises an energy transfer rod 640 and flange adaptor 650 disposed between the sonic head 210 and the drill rod 600. In this configuration, the seal 610 is disposed between the energy transfer rod 640 and the housing 300.

Standoffs provide strength and rigidity to the machine. Separate resonant modes do not occur within the machine's structure. For instance, each sonic head 200 is assumed to be a rigid body, and the standoffs 350 ensure that each mass acts as a rigid body during machine operation. The number of standoffs in the plurality can be selected to accommodate the size of the machine, such as between 1 and, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 75, or 100. A large machine typically contains more standoffs than a smaller machine for strength and rigidity. Each standoff 350 is matched with springs 410 and fasteners 351, so as the number of standoffs 350 increases, so do the number of springs 410 and fasteners 351.

FIG. 6 shows a resonance-enabled drill 100 with two voice coil actuators 500 coupled on the same side of a sonic head 210. Each voice coil comprises a coil assembly and a magnet assembly. A first coil assembly 510 and second coil assembly 520 are disposed on the housing 300. A first magnet assembly 515 and second magnet assembly 525 are coupled to the sonic head 210.

FIG. 7 shows a resonance-enabled drill 150 with a core barrel 660 and a corer bit 670 to take soil samples. The core barrel 660 is disposed on the proximal end to the sonic head 210. The corer bit 670 is disposed on the distal end of the core barrel 660.

FIG. 8 shows a resonance-enabled corer 150 with a core barrel 660, a corer bit 670, and two sonic heads 210,220. The first sonic head 210 is rigidly coupled to a first magnet assembly 515, a plurality of housing-to-first moving mass springs 410, a plurality of housing to second moving mass springs 420, and a plurality of first moving mass to second moving mass springs 430. The first sonic head 210 is further coupled to a housing ledge 312 by a plurality of housing-to-first sonic head springs 410 and to a second sonic head 220 by a plurality of first-to-second sonic head springs 430. The second sonic head 220 is coupled to the housing 300 via a plurality of housing-to-second sonic head springs 420 and the first sonic head 210 by a plurality of first-to-second sonic head springs 430. In certain embodiments, the first coil assembly 510 is rigidly coupled to the housing 300 and has little to no motion compared to the sonic heads 210,220.

FIG. 9 shows a resonance-enabled corer 150 with a core barrel 660 and corer bit 670 with a configuration to cancel forces to the housing 300 with opposing voice coils 500 to cancel resultant forces to the housing 300. In this embodiment, the first sonic head 210 is rigidly coupled to a first magnet assembly 515, a plurality of housing-to-first moving mass springs 410, a plurality of housing to second moving mass springs 420, a plurality of first moving mass to second moving mass springs 430. The first sonic head 210 is further coupled to a housing ledge 312 by a plurality of housing-to-first sonic head springs 410 and to a second sonic head 220 by a plurality of first-to-second sonic head springs 430. A first voice coil assembly 510 is disposed the top surface of the housing 300 inside the drill 150. The first voice coil assembly 510 is coupled to the first magnetic assembly 515.

The second sonic head 220 is coupled to the housing 300 via a plurality of housing-to-second sonic head springs 420 and the first sonic head 210 by a plurality of first-to-second sonic head springs 430. The second voice coil assembly 520 is disposed on the bottom surface of the housing 300 inside the drill 150, pointing in the opposite direction of the first voice coil 510. The second voice coil assembly 520 is coupled to the second magnetic assembly 525. If the housing springs 410,420 are not completely offset, they can be adjusted to cancel the resultant forces to the housing 300.

FIG. 10 shows the percent force with phasing two eccentric pairs from in-phase (0°) to out of phase (180°). The vector math for the resultant force of the pair of eccentrics is provided. The vector math represents the image in FIG. 11, which shows the phasor vector relation of the resultant force generated between two sinusoidal forcing functions from one force phased relative to the other. FIG. 12 shows a meter that displays the current state of the drill compared to the closest system resonance.

FIG. 13 shows the mode shape of (C) the displacement, (D) acceleration, and (E) stress of the drill system for (A) different lengths and (B) input frequencies. This example displays a single frequency and system length configuration, but its length and frequency may be adjusted. In certain embodiments, these plots represent angular displacement, angular acceleration, and angular stress for a corer rod undergoing torsional forces from the one or more sonic heads.

FIG. 14 shows the (B) displacement and (C) acceleration amplitudes of the head and bit versus the input frequency. The plots (A) may be swept through various lengths of pipe.

FIG. 15 shows a table of the undamped resonant frequencies of the penetration system relative to the number of added sections of drill pipe.

FIG. 16 shows (B) the plot of input power, useful power, wasted power, and power is delivered to the bit over the operating frequencies of the penetration system. (A) The length of pipes can also be selected. (C) Acceleration of the head and bit is also plotted on the lower axis and Input Power vs. Input Frequency.

FIG. 17 shows a plot indicating where resonance is located, stable operating conditions, and unstable operation conditions. With a hydraulic system driving spinning eccentrics, an unstable condition is encountered below resonance.

FIG. 18 shows the safe operating frequencies in white, where the operations conditions are shaded where the system stress state is too great, and failures will likely occur. The failures are caused by overstressing the system at various locations, which may cause instant failure, or the system may be fatigued prematurely.

Eccentrics

In certain embodiments, the force generator comprises one or more eccentrics. In certain embodiments, a motor drives each eccentric. In such embodiments, the motors are electrically synchronized. When a primary signal is generated, both motors are controlled by the primary signal. These motors counterrotate in relation to each other. Electric motors have not been used previously because the control system for electrically controlling motors to sync to one another has just recently been achieved. The industry has not understood that the current operating conditions are not recommended and could be improved using electric motors. One favorable operating condition is identified. It is often found below resonance, where the ratio of drill head motion amplitude over drill bit motion amplitude is minimal.

The drill bit generally moves more than the sonic head, permitting a higher transfer of power to the drill bit to drill. The drill may be unstable at this location and need less energy than at lower frequencies. The drill eccentrics rotational speed may increase, and the system is pulled through the favorable operating point. Therefore, with current technology, sonic drills may not be able to operate in such conditions.

In certain embodiments, the resonance-enabled drill comprises double eccentrics, such as four in total, with phase control. FIG. 36 shows an eccentric-driven sonic drill 100, where the eccentrics 530,540 are counterrotating and timed together. The resonance-enabled drill 100 comprised a housing 300, a sonic head 210 disposed within the housing 300, a plurality of eccentrics 530,540 disposed within the sonic head 210 and coupled to a motor 810 through a coupling 815, a drill rod 600 is coupled to the sonic head 210 at the proximal end. A drill bit 630 is coupled to the distal end of the drill rod 600. This drill 100 can be configured as a corer 150 for a single rod length for sampling.

FIG. 37 shows a dual electric motor drive 810,820 for a dual eccentric sonic drill 100. Each motor drives a single spinning eccentric. That is, motor 810 drives eccentric 530 through coupling 815, and motor 820 drives eccentric 540 through coupling 825. The eccentrics 530,540 in this embodiment are counterrotating and electrically synchronized.

FIG. 38 shows four electric motors 810,820,830,840 driving four eccentrics 530,540,550,560 in a sonic drill 100. The eccentrics 530,540,550,560 are organized into two paired sets of eccentrics, 530,540 and 550,560. Each motor drives a single spinning eccentric. That is, motor 810 drives eccentric 530 through coupling 815, motor 820 drives eccentric 540 through coupling 825, motor 830 drives eccentric 550 through coupling 835, and motor 840 drives eccentric 560 through coupling 845.

FIG. 39 shows the potential energy and kinetic energy changes of a resonant system of FIG. 21 as a function of time. The total amount of energy in the system is constant and no energy is absorbed within the system. FIG. 40 shows the energy when the resonant system of FIG. 21 operates at a frequency below mechanical resonance. At this state, the potential energy amplitude is greater than the kinetic energy amplitude and the system uses additional energy to balance the system. This additional energy is absorbed within the system during operation.

FIG. 41 shows a cross section view of a single electric motor 810 drive for a dual eccentric 530,540 sonic drill 100, comprising a rotor 685 between the sonic head 210 and the drill rod 600 and surrounded by a stator 680 and a stator housing 683. The eccentrics 530,540 are mechanically timed to each other. The rotor 685 and stator 680 drive the rotation of the drill rod 600. The rotor 685 and stator 680 can also be configured to drive torsional vibration of the pipe, allowing the pile 600 to not rotate but oscillate instead. The drill bit 630 oscillates rotationally. The torsional modes operate at different frequencies than the vertical oscillations, allowing the bit 630 to impact at different locations for each vertical oscillation.

FIG. 42 shows (B) a plot of displacement amplitude and (C) acceleration of the head and bit versus frequency. (A) The length of pipes can also be selected. The resonance conditions are displayed with a dashed line, and a potential operating point is defined as a long dash. The operating point has a recommended bit-to-head amplitude ratio, allowing energy to be delivered at the bit while minimizing the acceleration impact at the sonic head. Because this condition can be in the unstable operating range, standard hydraulically driven rigs cannot operate under this condition.

In certain embodiments, the resonance-enabled drill comprises two sets of counterrotating eccentrics. Each set spins at the same frequency, with one set, phased differently from the other set. In certain embodiments, at startup, the eccentrics are driven at 180° out of phase from one another, which cancels all vertical forces. The vertical force amplitude is adjusted by changing the phase between the two sets of eccentrics. As the eccentric's phase approaches 0°, the force approaches 100% force, which is the total force of the four eccentrics (m*r*ω²), where ‘m’ is the mass of the eccentric, ‘r’ is the distance from the center of rotation to the center of mass of the eccentric, and ‘ω’ is the angular speed of the eccentric rotation.

Commercially-available eccentric-driven drills use one set of eccentrics and operate at full force. In certain embodiments, the drill comprises a knob which an operator can use while drilling to adjust the input force amplitude to the drill. The operator can operate on or near resonance and then adjust the input force amplitude until the desired operating conditions are met. The adjustment of the input force amplitude changes the phase between the two pairs of eccentrics. The desired operating conditions include, but are not limited to, head acceleration, bit acceleration, input power, stress state within the system, penetration rate, energy transferred into and stored in various sub-systems, etc. The acceleration is related to the displacement, velocity, and jerk through the frequency of oscillation, and any of these can also be used. The stress state in the system can be maximum, mean, amplitude, etc.

In certain embodiments, torsional modes for the drill string use a rotary motor as the torsional driver. The torsional resonant modes are similar to the axial resonant modes. During operation, the torsional motor drives the oscillations at different frequencies, permitting the bit to impact at different rotational locations with each blow. The buttons on the bit hit virgin material and did not impact the same location. Also, the rotation oscillation acts as a paddle to loosen materials, such as clays, and move the loosened materials during drilling.

In certain embodiments, the drill comprises two classes of force generators, wherein the one or more voice coil actuators are tuned to a first frequency range and the one or more eccentrics are tuned to a second frequency range.

Drill Bit Plug

When drilling in soil, such as non-cemented clay, sand, and the like, the most common configuration for geotechnical drilling, the drill bit is selected accordingly. In these embodiments, the drill bit comprises tungsten carbide, steel with tungsten carbide inclusions or pellets, or the like. In certain embodiments, the drill bit is configured with an aggressive geometry to tear off and remove soil.

When encountering a boulder or hard layer, the conventional drill bit will be unable to progress and wear off rapidly. The sonic bit plug is a downhole wireline tool that latches into the bottom hole assembly (BHA) and expands underneath the conventional drill bit to the full string diameter or slightly more. Sonic motion is activated, and the pushdown force is applied to the drill string. The borehole can be progressed over a short penetration without rotation or circulation.

The sonic generator can be powered with air or fluid pressure or electric power.

In certain embodiments, rotation may remove the cuttings underneath the bit. The whole string can be gently rotated with a wireline bit-plug inside. Alternatively, the sonic bit plug could include a rotation capability, such as powered by electricity or air.

In certain embodiments, circulation cools the drill bit and evacuates the cuttings from the borehole. When present, circulation may be achieved through reverse circulation by injecting air at the bottom but inside the drill string at the top of the sonic bit plug. Reversed circulation is effective but may generate static pressure in the borehole slightly lower than the ambient hydrostatic, destabilizing the borehole. Reversed circulation cannot be applied to some types of soils, such as sand or highly fragmented rock. In certain embodiments, the sonic bit plug is pulled out of the borehole, and the borehole is cleaned up by gentle rotation with low Weight on Bit (WoB). In this instance, conventional fluid circulation and reaming may also be performed.

Interface

Commercially available drills have digital displays or analog displays that give the drilling operator the drill frequency and head acceleration but cannot be configured to display the resonance state. In certain embodiments, the resonance-enabled drill comprises a gauge configured to display information to the operator when the drill is on or near resonance. To be clear, the gauge continuously displays information, not just when the drill is on or near resonance. The gauge can indicate to the operator when the drill is operating on or near resonance. For example, the gauge displays to an operator where mechanical resonance is located compared to operating conditions of the drill. In certain embodiments, the drill is no longer at resonance and the gauges displays information on the stress state and safe operating conditions of the drill. In certain embodiments, the display comprises a list or visual cues of the current system setup's resonant frequencies. In certain embodiments, the display is digital, analog, or a combination thereof.

Commercially available drills do not indicate what the bit is doing. In certain embodiments, the resonance-enabled drill comprises a gauge configured to display the amplitude of the drill bit to the operator. The higher the drill bit motion, the better penetration. In these embodiments, the drill shows the bit amplitude to the operator. In certain embodiments, the resonance-enabled drill further comprises a secondary gauge configured to show the ratio of bit motion to the sonic head motion. In many situations, the operator is recommended to maximize this ratio. Commercially available drills only present the penetration rate and sound to the operator to describe the drill's vibratory state. These indicators are misleading because the sound is only generated by motion at the sonic head and is not a good indicator of bit motion.

Based on system parameters and the operating conditions, stress states are also estimated and configured to display on a gauge for the operator in certain embodiments. Failures are common because the readout to the operator is only at the sonic head. Still, with various drilling conditions, bit and bottom hole assembly configurations, and lengths and geometry of pipes, the stress states change. Therefore, the same amplitude of motion at the sonic head can generate drastically different stress conditions below ground.

The displays in commercially available drills show the total power delivered to the sonic head for performing work. The total power is broken into real and reactive power. The real power is what the system uses to do work, such as drilling. The reactive power drives the drill bit may be unused and reflected onto the driver, causing high power input. In certain embodiments, the resonance-enabled drill is configured to display the power components of the drill to the operator. These components include, but are not limited to, useful power, power delivered at the bit, power absorbed along the drill string's length, energy stored in the drill, and wasted power (reactive power).

During penetration, the drill bit may become a node, coupled with and fused to the workpiece. As the resonant condition changes, the resonance-enabled drill has a fixed node at the bottom of the string. When this occurs, the drill bit motion goes to zero or near zero, and penetration stops. When the penetration slows or ceases, the resonance-enabled drill is configured to display potential problems with options to remedy the lower-than-desired penetration rate. For example, when penetration is slowed or ceased, the resonance-enabled drill is configured to indicate to the operator that the weight on the bit should be reduced. In other saturations, the resonance-enabled drill may indicate when the weight on the bit is too great, causing potential fusing of the bit or damage to the workpiece if a sample is being taken. This indication may include a shift in the resonant frequency or be calculated from the drill's measurements. A list of resonant frequencies with the bit fused to the bottom also helps the operator because those are the resonant frequencies to operate on if the operator does not know what they are.

Based on the drilling configuration and system, the resonance-enabled drill is also configured to display safe operating frequencies for the operator in certain embodiments. If the operator tries to operate outside the safe operating ranges, then the resonance-enabled drill indicated such to the operator.

FIG. 26 shows a meter that displays the current state of the drill bit compared to decoupled and fusion. A recommended operating condition exists between the bit decoupled state (where the drill bit is not engaged with the workpiece) and fusion (where the drill bit acts as a node or fused to the workpiece). The indicator displays the system operator where the system is operating compared to the recommended conditions and if it is approaching bit decoupling or fusion. The displayed information is referred to as the critical weight on bit.

FIG. 27 shows a resonance-enabled machine configured as a drill with a voice coil-driven system at the sonic head. An internal force reflection mass 230 reacts to the opposing forces from the voice coil independent of the ground. The system uses the inertia of the reflection mass to react to the force imparted on the sonic head without transmitting the force to the housing.

Sensor

The sonic drill is a resonant system. When the system is operated on mechanical resonance, the system has a low impedance, which means it has a high resultant output compared to the input. The low impedance, allows the system to become a sensor and the system can be monitored through measurements than can be used to calculate changes in the boundary conditions, energy absorption, and damage to the system. An example, is when a force is applied at the sonic head that applies a very large weight on bit. The very large weight on bit is enough to fuse the bit with the soil. The boundary condition changes based on the new boundary condition at the bit. There will be a new resonant frequency based on the soil stiffness at the drill bit. The systems new measured phase between the input force amplitude and the resultant head acceleration oscillation can be used to calculate the soil stiffness at the drill bit.

The preceding description is given for clearness of understanding only. No unnecessary limitations should be understood, as modifications within the disclosure's scope may be apparent to those having ordinary skill in the art. Throughout the specification, where compositions are described as including components or materials, it is contemplated that the compositions can also consist essentially of, or consist of, any combination of the recited components or materials, unless described otherwise. Likewise, where methods are described as including steps, it is contemplated that the methods can also consist essentially of, or consist of, any combination of the recited steps, unless described otherwise. The disclosure illustratively disclosed herein suitably may be practiced in the absence of any element or step which is not specifically disclosed herein.

EXAMPLES Example 1

Referring to FIG. 8, the resonance-enabled corer operated at zero or near-zero alternating force transmitted to frame during operation. When operating the device of FIG. 8 with a measured ±60 g (±588 m/s²) of oscillation acceleration at the second sonic head and drawing an average of 120 W, the system cored a 1″ diameter (2.54 cm) hole with a 0.5 core in a 3″ thick (7.62 cm) piece of sandstone in under 3 minutes.

Example 2

Testing was performed on a GeoProbe™ 8150 LS using 40 ft of 4″ drill pipe and a coring bit. The coring was performed in a riverbed with various sizes of gravel, boulders, and sand. If too much weight was added to the bit by drill pipe, head weight, or push down force fusion was initiated at the bit.

FIG. 29 displays that when the sonic drill was operated at a nominally constant frequency of 120 Hz between 245 seconds and 250 seconds, the weight on the bit affected the system performance. Counterintuitively, less weight on a bit increased the penetration rate.

In FIGS. 30 and 31, the contrasting solid arrows XYX and dashed arrows XYZ show a higher penetration rate XYX was observed when the weight on bit was below the critical weight on bit. Conversely, when the weight on bit exceeded the critical weight on bit, the system's penetration rate decreased along with the subsequent acceleration. See FIG. 29.

FIG. 32 displays the relative push-and-pull forces from the hydraulic cylinder of the sonic drill that lift and push down the sonic drill. The observed critical weight on the bit line was displayed. Here, by reducing the weight on the bit, the resultant system acceleration increased, resulting in higher energy transfer to the bit for higher penetration rates.

FIG. 33 shows the resonance meter gauge readings during testing with a GeoProbe™ 8150 LS using 40 ft of 4″ drill pipe and a coring bit. As the frequency was increased from 60 Hz to operation at 120 Hz, the gauge went through resonance the drill was operated above resonance.

A gauge displays the difference between phase estimate from the model for the no coupling at the bit and the actual measurement. As the phase deviates, the gauge moves based on the coupling caused by the weight on the bit. The gauge has a cutoff between 5 and 45 degrees for the critical weight on bit. The gauge has a green zone between 0 and 45 degrees and, on some applications, a yellow zone between a value between 0 and 45 degrees and 45 degrees. After 45 degrees or the determined cutoff for the critical weight on the bit, the gauge will be red, indicating that the controller has exceeded the critical weight on the bit.

Example 3

Referring to FIG. 34, the sonic drill system was continuous with boundary conditions on each end. The boundary condition at the top of the drill string comprised the sonic driver internal force, sonic head mass, input force, damping force, and the air spring or isolator force. The top boundary condition can be expressed as Equation 1:

$\begin{matrix} {{E_{ds}A_{ds}\frac{\partial{u\left( {0,t} \right)}}{\partial x}} = {{m_{sh}\frac{\partial^{2}{u\left( {0,t} \right)}}{\partial t^{2}}} + {c_{ds}\frac{\partial{u\left( {0,t} \right)}}{\partial t}} + {k_{as}{u\left( {0,\ t} \right)}} - {F_{o}{\sin\left( {\omega_{f}t} \right)}}}} & {{Equation}1} \end{matrix}$

where m_(sh) is the mass of the sonic head, c_(ds) is the damping at the sonic head, k_(as) is the spring rate at the sonic head, F_(o) is the input force amplitude, ω_(f) is the input angular frequency of the input force, t is the time, u is the motion at any point along the x-axis, E_(ds) is the elastic modulus of the drill string, and A_(ds) is the cross-sectional area of the drill string.

The boundary condition at the bit end of the drill string comprised the bit mass and strata coupling internal force, strata damping force, and strata restoring force. The bottom boundary condition can be expressed as Equation 2:

$\begin{matrix} {{E_{ds}A_{ds}\frac{\partial{u\left( {L_{ds},t} \right)}}{\partial x}} = {{{- m_{db}}\frac{\partial^{2}{u\left( {L_{ds},t} \right)}}{\partial t^{2}}} - {c_{db}\frac{\partial{u\left( {L_{ds},t} \right)}}{\partial t}} - {k_{db}{u\left( {L_{ds},t} \right)}}}} & {{Equation}2} \end{matrix}$

where m_(db) is the mass of the drill bit, c_(db) is the damping at the drill bit, k_(db) is the stiffness at the drill bit, and L_(ds) is the length of the drill system.

The spring rate at the drill bit was minimal when the bit was free. The resonant frequency was lowest compared to when the bit interacted with the soil. Assuming different soil types of dense sand (1250 lbf*in⁻³ (3.38×10⁸ N*m⁻³)), extremely stiff clay (4680 lbf*in⁻³ (1.27×10⁹ N*m⁻³)), and granite (rock, 1.58×10⁶ lbf*in⁻³ (4.28×10¹¹N*m⁻³)). The equivalent spring rate onto the bit was the values above multiplied by the bit frontal area.

The phase between the input force at the sonic head and the resultant acceleration of the sonic head was measured. The critical weight on the bit was defined when the weight onto the bit during oscillation coupled with the soil/strata being drilled and the boundary condition at the bit changed because the soil stiffness acted onto the bit. If the bit were suspended, the bit impacted the soil/strata and did not couple but instead received quick transient impulses from the short contact with the strata each cycle. If the sonic drill were operating under the critical weight on the bit, the drill had equivalent phase readouts as the model without spring coupling at the bit for the drill during drilling operations. As the bit started to interact enough with the soil, where the soil stiffness acted as a boundary condition onto the sonic drill system at the drill bit, the resultant phase started to shift.

A commercial sonic drill has been modeled with 40 feet of drill pipe, a 2-foot stub, and a drill bit on the end. The sonic drill modeled with a minimal spring rate on the drill bit provided a measured phase reading similar to FIG. 34. At −90° of phase difference between the input force and the resultant acceleration at the sonic head, the system is on mechanical resonance (Point A on FIG. 34). The input force and velocity are in phase with one another. For this example, the system operated at ˜104.5 Hz. If the system is held operating at ˜104.5 Hz and additional downforce is applied, which applied more weight on the bit, the downforce may change if the soil stiffness coupling is enough.

When the weight on the bit was too great, the bit coupled with the soil or strata. The soil stiffness influenced the bit. If the weight on the bit was very great, the bit fully coupled to the soil or strata, and the soil stiffness acted as a spring on the bit. Here, the bit fused onto the soil and became a node. This transition took the bit from a freer boundary condition to a fixed boundary condition. If the soil or strata is rock, the soil stiffness is so great that it allows no motion at the bit.

If the soil is dense sand and enough weight on bit is applied that the drill bit is fused with the soil so that all the soil stiffness is pushing on the drill bit, then the boundary of the system changes and the measured phase changes based on the soil stiffness. At the point of fusing with dense sand, the measured phase reads −46°, shifted from Point A to Point B in FIG. 34, while the system is still operating at the same frequency. The system's resonant frequency has shifted up to 106.5 Hz by changing the boundary condition. With the bit fused, the system has lost the ability to dissipate energy by drilling through the strata. Instead, the system has to dissipate the energy within the system. In many cases, the system cannot dissipate energy, and the oscillations grow until failure occurs. If the soil stiffness is greater than dense sand, as with stiff clay, the same conditions will occur, but the phase shift is greater than that of dense sand.

With stiff clay, the resonant frequency can shift from 104.5 Hz to 112 Hz, and the phase measured at 104.5 Hz now drops to −10°, a shift from Point A to Point C in FIG. 34. Hard rock is an extreme case. If drilling through granite, the phase will shift above the 150 Hz operating range of the drill, and the phase will be within 10° of −180° out of phase, which is the case when the system is very far from mechanical resonance, shift from A to D in FIG. 35.

From these plots, with soils with lower soil stiffness, sands, and low stiffness clays, the weight applied to the bit can be greater than the systems with large soil stiffness, high stiffness clays, and rock. Because the system behaves similarly with the low weight on the bit with the low stiffness clays and sands, whereas pushing up to the critical weight on bit allows motion at the drill bit to perform drilling, and the system performs as intended with a free boundary condition at the drill bit. However, with stiff clays, the weight on the bit needs to be more closely monitored. After all, it can become fused, and then the drill will be in a refusal state where the bit cannot move because it has fused to the boundary condition. The resonant condition has shifted, but the resonant condition is the new boundary condition where the bit is fused with the strata, making it impossible to uncouple the drill bit from the strata once fusing has. As the soil stiffness increases, less weight on bit is required for fusing. Therefore, less weight on bit should be used when drilling through stiff clays than sands and even less weight when drilling through rock than clays.

If the weight on bit is intentionally applied large enough to provide fusing of the drill bit to the soil, then the drill system may be used as a sensor to detect the change in system response of phase difference between the input force and the resultant acceleration at the sonic head to determine the soil stiffness. In FIG. 34, the system responses change because of the soil type and this method was described above to determine the critical weigh on bit, but the measured phase can be used to calculate the soil stiffness. One such method is to create a curve of the change is drill phase performance vs. the soil stiffness and this can be used to determine the type of soil at the drill bit.

The practice of a method disclosed herein, and individual steps thereof, can be performed manually and/or with the aid of or automation provided by electronic equipment. Although processes have been described concerning embodiments, a person of ordinary skill in the art will readily appreciate that other ways of performing the methods' acts may be used. For example, the order of various of the steps may be changed without departing from the method's scope or spirit unless described otherwise. Some of the individual steps can also be combined, omitted, or further subdivided into additional steps.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. All patents, publications, and references cited herein are fully incorporated by reference. In case of conflict between the present disclosure and incorporated patents, publications, and references, the present disclosure should control. 

1. A resonance-enabled drill, comprising: a housing; one or more force generators chosen from one or more voice coil actuators, or one or more eccentrics driven by one or more electric motors; one or more sonic heads coupled to the one or more force generators; a plurality of springs coupling the housing to the one or more sonic heads; and a drill rod disposed on its proximal end to the one or more sonic heads.
 2. The drill of claim 1, further comprising a bit disposed on the distal end of the drill rod.
 3. The drill of claim 1, wherein the one or more voice coil actuators comprise a coil assembly rigidly disposed on the housing or on a reflection mass and a magnet assembly disposed on the one or more sonic heads.
 4. The drill of claim 3, wherein the coil assembly of each of the one or more voice coil actuators has little to no motion compared to the one or more sonic heads.
 5. The drill of claim 1, wherein each eccentric is driven by one electric motor.
 6. The drill of claim 5, wherein the one or more force generators comprises two paired sets of eccentrics configured to exert no vertical force, using a 180° phase angle between the two paired sets of eccentrics.
 7. The drill of claim 6, wherein the one or more force generators comprises two paired sets of eccentrics configured to exert full vertical force, using a 0° phase angle between the two paired sets of eccentrics.
 8. The drill of claim 1, further comprising a seal disposed between the housing and the drill rod.
 9. The drill of claim 1, further comprising a spring-damper disposed between the drill rod and the bit.
 10. The drill of claim 9, wherein the spring-damper cushions impact of the drill bit by widening and lowering impulse magnitude, whereby transfer of primary resonant energy to unwanted resonant modes is lowered, and the drill bit is kept in motion and not fused with a workpiece.
 11. The drill of claim 1, further comprising an energy transfer rod and flange adaptor disposed between the one or more sonic heads and the drill rod.
 12. The drill of claim 1, further comprising between the one or more sonic heads a rotor disposed on the drill rod, and a stator and stator housing disposed on the housing.
 13. The drill of claim 1, wherein the kinetic energy stored in the drill by the one or more sonic heads is directly offset by potential energy stored within the plurality springs.
 14. The drill of claim 1, further comprising a reflection mass coupled to the one or more sonic heads through a second plurality of springs and configured to offset the kinetic energy stored in the drill.
 15. The drill of claim 1, wherein the housing comprises a plurality of plates and a plurality of standoffs.
 16. The drill of claim 1, having a resonance frequency, and, when the drill is on resonance, an input force is in phase with the resultant oscillation velocity of the one or more sonic heads.
 17. A gauge for a sonic drill configured to display information to an operator when the drill is on or near resonance, wherein the information comprises one or more parameters chosen from an amplitude of the drill bit, a resonant frequency of the drill, a stress state, power components of the drill, and safe operating frequencies. 18-24. (canceled)
 25. A method for selecting a resonance frequency in a sonic drill comprising a force generator, one or more sonic heads, and a gauge, the method comprising: measuring phase between the force generator and the one or more sonic heads in the sonic drill; and displaying resonance on the gauge to indicate the resonance frequency of the drill based on the phase.
 26. (canceled)
 27. (canceled)
 28. The method of claim 25, when the sonic drill comprises a bit, the method further comprises maximizing the ratio between bit motion and motion of the one or more sonic heads.
 29. The method of claim 25, further comprising, when the sonic drill comprises a bit and penetration of the bit is slowed or ceased, reducing the weight on the bit to adjust the resonance frequency of the drill to continue drilling. 30-36. (canceled) 